1. Field of the Invention
This invention pertains to the general field of surface profiling and apparatus for aligning a sample surface to a template that defines regions of special interest. In particular, the invention provides a novel approach for matching the regions of interest in a test part to a corresponding template in order to effect the alignment of the part, and further utilizes the template for correcting measurement errors resulting from material and wavelength variations between adjacent regions in the part.
2. Description of the Prior Art
Parts that are measured by surface profilometry for quality control often contain distinct regions separated by a boundary delineating different properties, such as materially different heights, for example. The surface characteristics of some of these regions may be critical to the performance of the part, while others may be totally irrelevant. Therefore, it is typically preferable to measure only the regions of interest. Moreover, since speed of measurement is often an important aspect of this kind of testing, limiting the measurement to the regions of interest also enhances the efficiency of the testing procedure.
Copending U.S. Ser. No. 09/585,370, herein incorporated by reference, describes a method of alignment of a template utilized to identify the regions of interest on the surface of the test part. The method provides an electronic template representing the topography of the part being tested (i.e., a magnetic head) and delineating distinct patterns corresponding to particular regions of interest (such as ABS surfaces), so that analysis of the sample's surface can be limited to those regions. According to one aspect of the invention, the outline of the part positioned in a plastic tray within the field of view of an interferometric microscope is identified by measuring the modulation of incident light at each pixel inside and outside the contour of the part using the loci of perceivable fringe contrast as the criterion for establishing the location of the part edges. Once the outline of the part within the plastic tray is so established, the position of the part is shifted within the field of view coordinates to match the template, thereby automatically achieving a precise alignment of the template with the boundary of the slider. In turn, the template patterns also become aligned with the regions of interest in the test part and interferometric analysis can be limited to data corresponding to the pixels contained within those patterns.
As a result of this technique, the regions of interest in the test part are quickly identified and tested, avoiding the unnecessary steps of analyzing the remaining regions of the sample. According to another aspect of referenced invention, curve-fitting schemes are used to facilitate and expedite the process of identifying the contour of the test part. In the case of conventional magnetic-head sliders, which are substantially rectangular in plan view, straight-line fitting between a few data points along two adjacent edges is sufficient to find the location of the edges and the corner between them, which in turn can be used is straightforward manner to align the template with the slider.
The present invention is a further development in the art directed at generalizing the concepts disclosed in Ser. No. 09/585,370 to different profilometric techniques and to test surfaces having regions separated by distinct physical properties.